There has been known the cooling structure of a hollow conductor in a high-voltage bushing of a rotating electric machine disclosed in the following Publications. For example, Jpn. Pat. Appln. KOKOKU Publications No. 60-16180, 5-17780 and Jpn. Pat. Appln. KOKAI Publication No. 5-207701 are given.
One example of the cooling structure of a hollow conductor included in a high-voltage bushing of a rotating electric machine will be explained below with reference to FIG. 16 and FIG. 17. FIG. 16 is a view showing the basic structure of a rotating electric machine. FIG. 17 is a view showing the structure of a conventional high-voltage bushing included in a rotating electric machine.
For example, in a large-capacity turbine generator, a hydrogen gas is sealed in a rotating electric machine shown in FIG. 16. The hydrogen gas is used as a cooling medium (coolant) to cool a rotor 1, a stator core 2, a stator coil 3, and the like. A connection from the stator coil 3 to a high-voltage bushing 6a attached to an output terminal box 5 is made by way of a conductor 4 to fetch an electric output outside a rotating electric machine. Moreover, if the stator coil 3 is star-connected to ground its neutral point, an electric output is fetched outside by way of a high-voltage bushing 6b attached to the output terminal box 5 to make a neutral connection. In this case, the output terminal box 5 is attached to a stator frame 7. The foregoing high-voltage bushings 6a and 6b lead a cooling gas 11 into these each bushing to perform cooling.
A high-voltage bushing shown in FIG. 17 has a hollow conductor 8 and an insulator tubeinsulator tube 9 such as an insulator. Specifically, the hollow conductor 8 is attached to a terminal box 5 in state of penetrating the box 5 to fetch an output of a rotating electric machine. The insulator tubeinsulator tube 9 is attached to the outer circumferential side of the hollow conductor 8 to insulate the hollow conductor 8 from the terminal box 5. Further, the insulator tubeinsulator tube 9 has a flange and a seal portion, and is fixed to the terminal box 5. In general, the flange is made of metal, and integrally formed with an insulating portion using a bonding agent.
The hollow conductor 8 penetrates the insulator tubeinsulator tube 9 so that an outside conductor connection part 15 is formed, and is connected to a current lead outside a rotating electric machine. Further, the hollow conductor 8 is fixed to the insulator tubeinsulator tube 9 in a state of forming a clearance by means of a conductor retainer 13. Sealing is provided using a packing 10 so that a cooling gas 11 in the machine is prevented from leaking from a joint portion of the hollow conductor 8 and the insulator tubeinsulator tube 9. Furthermore, the hollow conductor 8 has a structure that a machine-external side end portion 12 is sealed.
The hollow conductor 8 is heated because a large current is carried therein; for this reason, the hollow conductor 8 is cooled by taking the cooling gas 11 of a rotating electric machine therein. Specifically, the cooling gas 11 of the machine is guided into a high-voltage bushing from a notch portion formed in a conductor retainer 13. Then, the cooling gas 11 flows through the clearance between the hollow conductor 8 and the insulator tubeinsulator tube 9, and thereafter, flows outside the machine. In this way, the cooling gas 11 cools the outer circumferential surface of the hollow conductor 8. The cooling gas 11 cooling the outer circumferential surface of the hollow conductor 8 is guided to an inner circumferential side of the conductor 8 by way of a plurality of communicating holes 14 formed in the conductor 8. In this case, each direction (i.e., direction to which the cooling gas 11 is injected) of these communicating holes 14 is vertical to the wall surface of the hollow conductor 8. The cooling gas 11 guided to the inner circumferential side of the hollow conductor 8 flows toward the machine-side end portion of the hollow conductor 8. In this way, the inner circumferential surface of the hollow conductor 8 is cooled. The cooling gas 11 cooling the inner circumferential surface of the hollow conductor 8 is exhausted from the machine-side end portion of the hollow conductor 8.
An inner-diameter side flow passage of the hollow conductor 8 is connected to a portion of a rotating electric machine lower than a cooling gas voltage in the output terminal box 5 given as an inlet side of the cooling gas of a high-voltage bushing, for example, to a fan inlet low-pressure chamber by way of a pipe (not shown). The differential pressure between the foregoing both pressures is used as a drive force so that the cooling gas 11 flows in the high-voltage bushing as described above. In this way, heat generated in the hollow conductor 8 is cooled.
A high-voltage busing has a structure of penetrating the stator frame 7 of the rotating electric machine; for this reason, the high-voltage bushing must be sealed so that a hydrogen gas does not leak outside the machine. In general, a packing 10 (or gasket) used as a seal portion is exposed in high temperature; for this reason, the packing 10 is aged. As a result, the packing 10 does not perform a gas seal function. Therefore, the seal portion needs to make a design so that the seal portion is sufficiently cooled and does not become high temperature.
However, according to the structure of the conventional high-voltage bushing, the external conductor connection part 15 has a projected structure of penetrating the insulator tubeinsulator tube 9. On the other hand, the communicating hole 14 for carrying the cooling gas 11 must be provided inside the insulator tubeinsulator tube 9 considering the flow passage configuration of the cooling gas 11. For this reason, when flowing through the communicating hole, the cooling gas 11 returns soon, and thereafter, flows into the machine. As a result, the flow of the cooling gas 11 stays in an area positioning outside the machine from the communicating hole 14. Therefore, sufficient cooling is not performed; for this reason, the hollow conductor 8 becomes high temperature.
In addition, the cooling gas seal must be given at a position outside the machine from the communication hole 14. For this reason, the packing 10 contacts with high temperature hollow conductor 8; as a result, the packing 10 is aged. Therefore, a hydrogen gas easily leaks.